Detection of network security breaches based on analysis of network record logs

ABSTRACT

Computer program products and methods of inspecting a log of security records in a computer network are provided. The method includes retrieving a log record, processing the log record including deriving a key to a table, determining a data value from information in the log record and adding the data value to a list of data values associated with the key if the data value is unique. One or more entries of the table are evaluated based on predetermined criteria to detect attempted security breaches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/951,518, filed Dec. 6, 2007, which is a continuation of U.S. patentapplication Ser. No. 10/407,823, filed Apr. 4, 2003, now U.S. Pat. No.7,325,002, the disclosures of which are incorporated by referenceherein.

BACKGROUND

The present invention relates to a method for controlling computernetwork security.

Firewalls and intrusion detection systems are devices that are used toprotect a computer network from unauthorized or disruptive users. Afirewall can be used to secure a local area network from users outsidethe local area network. A firewall checks, routes, and frequently labelsall messages sent to or from users outside the local area network. Anintrusion detection system (IDS) can be used to recognize suspiciouspatterns of behavior in a communication system. Examples of an intrusiondetection system include a network intrusion detection system (NIDS) anda host intrusion detection system (HIDS). A NIDS can be used to examineinformation being communicated within a network to recognize suspiciouspatterns of behavior. A HIDS can be used to examine information beingcommunicated through a particular host computer within a network torecognize suspicious patterns of behavior. Information obtained by theintrusion detection system (IDS) can be used to block unauthorized ordisruptive users from accessing the network.

Either a firewall or an intrusion detection system can create logrecords that record incoming and outgoing events into or out of anetwork. Log records can include events such as security violations,bandwidth usage, email usage, and employee access to the Internet.Typically, these log records are reviewed by network securityadministrators in order to detect attempted security breaches or to findtrends in traffic patterns. Since the number of log records is typicallyquite large, query languages are often used to analyze the log recordsto detect attempted security intrusions. Query languages can also beused to analyze the log records and generate reports summarizing theselog records for the network administrator. These reports can be used bythe network administrator to respond to a recognized network securityintrusion. Query language instructions operating on log records can alsobe used to generate alerts for the network administrator. Since thenumber of log records can be quite large, the network security solutionsutilizing query language instructions to analyze the log records can beslow. Query language based solutions can be slow when all the logrecords are analyzed every time a new query is received.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus, includingcomputer-products for detecting attempted network security breaches. Inone aspect, the invention provides a method of inspecting a log ofsecurity records in a computer network and includes retrieving a logrecord, processing the log record including deriving a key to a table,determining a data value from information in the log record and addingthe data value to a list of data values associated with the key if thedata value is unique. The method includes evaluating one or more entriesof the table based on predetermined criteria to detect attemptedsecurity breaches.

Aspects of the invention can include one or more of the followingfeatures. The table can be a hash table. The list of data values can beimplemented as a linked list. The list of data values can be implementedas a hash table. The list of data values can be implemented as a tree.Evaluating one or more entries of the table can include evaluating allof the entries of the table.

In another aspect, the invention provides a method of inspecting a logof security records in a computer network and includes retrieving a logrecord, hashing one or more of the fields of the log record to generatea hash key, and evaluating a hash table using the hash key. If there isno matching hash table entry, the method includes adding a new entry tothe hash table. If there is a matching hash table entry, the methodincludes retrieving a data list associated with the hash table entry andusing one or more fields of the log record to compute a data value to beinserted into the data list, evaluating the data list to determine theuniqueness of the data value and inserting the data value in the datalist if the data value is unique.

In another aspect, the invention provides a method of detecting a portscan and includes retrieving a log record including a source address anda destination address, hashing the source address and the destinationaddress to generate a hash key and evaluating a hash table using thehash key. If there is a matching hash table entry, the method includesretrieving a data list to determine if there are any matching entries,inserting the destination port with the entries in the data list ifthere are no matching entries and determining a port scan if the numberof items in the data list exceeds a predetermined number.

In another aspect, the invention includes the computer program productsfor causing a computer to execute instructions to cause data processingapparatus to retrieve a log record, process a log record includingderiving a key to a table, determine a data value from information inthe log record and add the data value to a list of data valuesassociated with the key if the data value is unique. One or more entriesof the table are evaluated based on predetermined criteria to detectattempted security breaches.

Aspects of the invention may include one or more of the followingadvantages. The table may be a hash table. The list of data values maybe implemented as a linked list. The list of data values may beimplemented as a hash table. The list of data values may be implementedas a tree. Instructions to evaluate one or more entries of the table mayinclude instructions to evaluate all the entries of the table.

In another aspect, the invention includes the computer program productsfor causing a computer to execute instructions to cause data processingapparatus to retrieve a log record, hash one or more fields of the logrecord to generate a hash key, and evaluate a hash table using the hashkey. If there is no matching hash table entry, the invention may allowthe addition of a new entry to the hash table. If there is a matchinghash table entry, the invention may allow retrieval of a data listassociated with the hash table entry, use of one or more fields of thelog record to compute a data value, comparison of the data value withentries in the data list to determine if there are any matching entries,inserting the data value into the data list if there are no matchingentries, and evaluating the data list based on predetermined criteria todetect attempted security breaches.

Aspects of the invention may include one or more of the followingadvantages. The invention may include instructions for adding a newentry to the hash table causing the data processing apparatus togenerate an empty data list associated with the new entry to the hashtable, instructions for inserting a new entry in the data list cause thedata processing apparatus to trigger the evaluation of the data list,instructions for issuing a check table operation causing the dataprocessing apparatus to trigger the evaluation of the data list,instructions for evaluating the data list based on predeterminedcriteria causing the data processing apparatus to block a packetassociated with the log record, instructions for evaluating the datalist based on predetermined criteria causing the data processingapparatus to block all future packets from a same source as a packetassociated with a given log record and instructions for evaluating thedata list based on predetermined criteria causing the data processingapparatus to report an attempted security breach.

The data list may be a linked list. The data list may be a hash table.The data list may be a tree. The invention may include instructions forevaluating the data list causing the data processing apparatus toevaluate the data list after a plurality of log records have been addedto the data list. The invention may include instructions for evaluatingthe data list causing the data processing apparatus to evaluate the datalist after each log record is added to the data list. The invention mayinclude instructions for evaluating the hash table using the hash keycausing the data processing apparatus to process a second hash table.The invention may include instructions for processing a second hashtable causing the data processing apparatus to use the matching hashtable entry to retrieve a second hash table, and using the hash key toevaluate the second hash table. If there is no matching second hashtable entry, the invention may allow the addition of a new entry to thesecond hash table. If there is a matching second hash table entry, theinvention may allow retrieval of a second data list associated with thesecond hash table entry, comparing the data value with entries in thesecond data list to determine if there are any matching entries,inserting the data value in the second data list if there are nomatching entries and evaluating the second data list based onpredetermined criteria to detect attempted security breaches.

In another aspect, the invention, embodied in an information carrier forinspecting a log of security records in a computer network includes acomputer program product for causing the computer to executeinstructions to cause the data processing apparatus to retrieve a logrecord, hash one or more fields of the log record to generate a hash keyand evaluate a hash table using the hash key. If there is no matchinghash table entry, the invention allows adding a new entry to the hashtable. If there is a matching hash table entry, the invention allowsretrieving a data list associated with the hash table entry, using oneor more fields of the log record to compute a data value to be insertedinto the data list, evaluating the data list to determine the uniquenessof the data value and inserting the data value in the data list if thedata value is unique.

In another aspect, the invention, embodied in an information carrier fordetecting a port scan, includes a computer program product for causing acomputer to execute instructions to cause the data processing apparatusto retrieve a log record including a source address and a destinationaddress, hash the source address and the destination address to generatea hash key, and evaluate a hash table using the hash key. If there is amatching hash table entry, the invention allows retrieving a data listassociated with the hash table entry, comparing the destination portwith the entries in the data list to determine if there are any matchingentries, inserting the destination port into the data list if there areno matching entries and determining a port scan if the number of itemsin the data list exceeds a predetermined number.

Advantages of the invention may include one or more of the followingfeatures. Each log record needs to be processed only once when it isfirst received. The analysis of log records can be fast because a hashtable is used to store and retrieve the log records. Storing theprocessed log records instead of the log record itself can require lessmemory capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a network topology including a NIDS operating in inlinemode.

FIG. 1B shows a network topology including a NIDS operating innon-inline mode.

FIG. 2 is a flowchart describing the operation of a record processingunit.

FIG. 3 is a flowchart for building a table in static mode.

FIG. 4 is a flowchart for building a table in dynamic mode.

FIG. 5 describes a table data structure.

FIG. 6 is a flowchart for creating a table data structure.

FIG. 7 is a flowchart for evaluating the table data structure.

FIG. 8 illustrates the use of multiple hash tables.

FIG. 9 illustrates the use of cascaded hash tables.

FIG. 10 shows a method for detecting a port scan attack.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1A shows a network topology including a local area network (LAN)100, including a server 102, several workstations (W/S) 104, a firewall106, and NIDS 108. The NIDS 108 operates in inline mode and analyzesinformation as it is being communicated in the network. The LAN 100 isconnected to an external network, e.g., the Internet 114, through thefirewall 106. The LAN 100 is also connected to a second LAN 116 througha router 118, and satellite 120. Second LAN 116 includes a web server110, an email server 112, a server 102, several workstations 104, afirewall 106 and NIDS 108. The computers, servers and other devices inthe LAN are interconnected using a number of data transmission mediasuch as wire, fiber optics, and radio waves. Each LAN uses intrusiondetection systems to analyze messages being communicated within thenetwork and recognize suspicious patterns of behavior. Each LAN 100 and116 includes a record processing unit 122 connected to firewall 106 andNIDS 108. The record processing unit (RPU) 122 receives log records fromone of firewall 106 and NIDS 108 and analyzes the log records to detectattempted network security intrusions. Alternatively, the NIDS can beconfigured outside the transmission path, in a passive (non-inline)mode. In the non-inline mode, the NIDS device monitors and inspectstraffic received by the network, but only reports (i.e., does not droppackets) that are determined to match specified attack signatures. FIG.1B shows a network topology including NIDS 124 operating in non-inlinemode. The NIDS 124 receives information being communicated in thenetwork, determines attacks and can report or otherwise passively act toblock future communications from unauthorized or disruptive users.

FIG. 2 is a block diagram of the RPU 122. The RPU 122 includes aninterface 202 for communicating (e.g. to firewalls, and intrusiondetection systems) with one or more security devices on the network.Interface 202 is used to receive security logs. The RPU 122 uses aprocessing engine 204 to process security logs received from thesecurity devices on the network. The processed log records are stored ina database 208. An evaluation engine 206 uses the processed log recordsstored in the database 208 to detect attempted network securitybreaches. Any attempted network security breaches detected by RPU 122can be communicated to a respective security device using interface 202.

RPU 122 can be operated in at least two different modes. In the firstmode, a plurality of log records are received and processed. The firstmode is referred to as the off-line mode. In the second mode, the RPUreceives and processes individual log records as they are generated. Thesecond mode is referred to as the on-line mode.

FIG. 3 is a flow diagram describing the off-line mode of operation. Inthe off-line mode, a log of records is communicated to the RPU 122. Thelog can be produced by security devices on the network based on incomingor outgoing communications. The RPU 122 receives the log records (step300) and retrieves individual records (step 302) for processing. The logrecord is used to build and update a table data structure (step 304). Ifthere are additional log records that need to be processed (step 306)control passes to step 302 at which time the process repeats and thenext log record is processed. In one implementation, the table datastructure is evaluated (step 308) after all the log entries have beenprocessed and RPU 122 responds if any attempted security intrusion isdetected (step 310). In response to an attempted security intrusion, theRPU 122 can communicate the attempted security intrusion to the securitydevice (e.g. firewall, IDS) or other devices on the network. In oneimplementation, RPU 122 can block all future packets from the sourceresponsible for the attempted intrusion (e.g., by communicating a ruleto the firewall to block all packets from the responsible source). RPU122 can also report the attempted security intrusion to theadministrator for an appropriate response.

FIG. 4 is a flow diagram describing the on-line mode of operation. Inthe on-line mode, individual log records are received by RPU 122 forprocessing (step 400). In the on-line mode, RPU 122 processes individuallog records as they are received. The processed log records are used toupdate the table data structure (402) and the resulting table datastructure is evaluated (404) after each log record is processed.Thereafter, RPU 122 responds to any attempted intrusion (406) before RPU122 starts processing the next log record.

FIG. 5 describes one example of a table data structure used by RPU 122.Referring now to FIGS. 2 and 5, a hash key 512 generated by theprocessing engine 204 from the fields of the log record, is used togenerate an address for an entry in the hash table 500 using a tableaddress generator 508. The address generated by the table addressgenerator 508 is used to look up the selected entry in hash table 500.Each hash table entry can either be a data value 502, a list of datavalues 504, a pointer to a data value or a data list 506. Entries thatconsist of a data value or a set of data values (502 or 506) can bestored directly in the hash table 500 in database 208. For data lists,the hash table entry can be a pointer to the data list 506 in database208. The data list 510 contains a list of data values and can beimplemented using a linked list or any other suitable data structure.

The data entries in hash table 500 and the data list 510 can be taggedto expire after a predetermined duration of time. A timer 509, can beused by the processing engine to measure a specific duration time for agiven data entry stored in the hash table or data list. The data entrycan be deleted when the time duration has expired. One simple timerimplementation includes the tagging of each entry with a time stamp. Atevaluation time, the current time can be compared to the stamped time.Entries that are too old can be removed prior to the evaluation step.

FIG. 6 is a flow diagram depicting the creation of the table datastructure. RPU 122 (FIG. 1 a) receives one or more logs (step 600) fromone or more security devices on the network. Individual log records areretrieved (step 602) and the fields of the log record are used togenerate a hash key (step 604). The generated hash key is used toevaluate a hash table (step 606). If a matching entry is found in thehash table (step 608) a data list associated with the selected hashtable entry (step 610) is retrieved. A data value generated using one ormore fields of the log record (step 624), is compared with the datavalues in the data list (step 612). Only unique data values are insertedinto the data list. If a matching entry is found in the data list (step614), the data value derived from the log record is not inserted intothe data list (step 616). If no matching entry is found in the datalist, the data value is inserted into the data list (step 618) andcontrol passes to step 602 at which time the process repeats and thenext log record is processed. If no matching entry is found in the hashtable during step 608, a new hash table entry and a new data list arecreated (step 620). The new data list is associated (step 622) with thehash table entry indicated by the generated hash key and the data valuegenerated using the fields of the log record (step 624) is inserted intothe data list (step 618). Following the completion of step 618 controlpasses to step 602 at which time the process repeats for each log recordreceived.

FIG. 7 is a flow diagram describing a process of evaluating a hash tableto detect attempted security breaches. The table data structure can beevaluated whenever a new entry is added to a hash table or to a datalist that is part of the table data structure. In addition, a “CheckTable” operation, initiated by a user, can also trigger an evaluation ofthe table data structure. In one implementation, the table datastructure is evaluated by retrieving each hash table entry (step 700).If the entry is a pointer to a data list (step 702) the data list isretrieved (step 704). If the table entry contains a data value or a setof data values these values are retrieved (step 706). The data valuesretrieved in step 704 or step 706 are compared against predeterminedcriteria to determine if there has been an attempted security breach(step 708). If an attempted intrusion is detected, RPU 122 can take oneof a plurality of actions based on the nature of the attempted breach(step 710). RPU 122 can communicate with the NIDS or firewall to dropthe current packet associated with the log record. RPU 122 can alsoblock all future packets originating from the same source in response toan attempted security breach. In addition, RPU 122 can report anyattempted security breach to the administrator for appropriate response.This process is repeated for all the entries in the hash table.

In an alternative implementation of the hash table evaluation process,only table entries that have been modified after the previous tableevaluation are considered during the evaluation process. This can beaccomplished by including tag fields in the hash table entry to indicateany entries that are modified as a result of inserting a new data valuein the table data structure. The tag field is used to locate modifieddata values during the table evaluation process. The tag fields can bereset after the modified data has been used to evaluate the table. Inanother implementation of the hash table evaluation process, the hashtable is evaluated immediately after inserting a new data value in thetable data structure (i.e., right after step 618 above in FIG. 6).

RPU 122 can employ more than one hash table. FIG. 8 illustrates anexample using more than one hash table to detect an attempted securityintrusion. In the example, a log record is obtained by RPU 122 duringeither the on-line or off-line mode of operation (step 800). Anevaluation strategy is determined using the log record, a hash keygenerated from the log record, or a combination of the log record and ahash key derived from the log record (step 805). The evaluation strategycan be used to identify the number of tests and the type of tests thatshould be performed for the given record. The evaluation strategy can bebased on a number of criteria including, known attack signatures andprior log records originating from the same source. A number of hashkeys are generated, based on the evaluation strategy, for the differenttype of tests that must be performed (step 815). The generated hash keysare used to update the hash tables associated with the tests to beperformed (step 820). The hash tables associated with the tests areevaluated to determine if there has been an attempted security intrusion(step 825). In this example, all the hash keys and all the hash tablesmay not be distinct. It is possible to use the same hash key to updateand evaluate two different hash tables. It is also possible to use twodifferent hash keys to evaluate the same hash table as part of twodifferent tests.

FIG. 9 illustrates an example using cascaded hash tables to detect anattempted security intrusion. In this example, as part of the tableevaluation process, a first hash table entry is retrieved from a firsthash table. The first hash table entry is checked by comparing the firsthash table entry against a predetermined criteria (step 900). Theevaluation process for detecting a particular security intrusion mayrequire the evaluation of a second hash table. A second hash key for thesecond hash table can be generated using the first hash key, the firsthash table entry selected by the first hash key, or a combination of thefirst hash key and the first hash table entry selected by the first hashkey (step 905). The second hash table is updated using the second hashkey (step 910) and the second hash table is evaluated to determine ifthere has been an attempted security intrusion (step 915). Theevaluation of the individual hash tables is as described above withrespect to FIG. 6.

FIG. 10 shows an exemplary method for detecting a port scanning attack.Port scanning, a frequently used approach for attacking computersecurity, gives a hacker an idea where to look for weaknesses. A portscan comprises a series of messages sent by the hacker attempting toprobe a computer to learn which computer network services, eachassociated with a “well-known” port number, the computer provides.Essentially, the port scan consists of sending a message to each port,e.g., one at a time. The kind of response received indicates whether theport is used and accessible and can therefore be probed for weaknesses.In the present example, a log of records that include port queries isevaluated. The log can be generated by a router, firewall or othersecurity device. RPU 122 extracts the source and destination IPaddresses from the log records received (step 1000). The source anddestination IP addresses as reported by the log record are used togenerate a hash key (step 1005). The generated hash key is used by atable address generator 1010 to evaluate a first hash table 1015. RPU122 adds any unique port numbers accessed by the application to the datalist 1025 indicated by the hash table entry 1020 selected by thegenerated hash key. During a typical port scan attack, the data list1025 accumulates a large number of entries as the hacker attempts toaccess a large number of ports within a short time interval. Each portnumber added to the data list 1025 can be tagged to expire after apredetermined duration of time, for example, using the timer 509 (FIG.5). Once the data list 1025 accumulates a predetermined number ofentries, a port scan is detected. The source and destination IPaddresses included in the hash key can be used to determine the sourceof the scan and the computer that is being scanned.

In another example, the techniques disclosed can be used to detect amail server attack. A typical mail server attack can proceed in threephases. During the first phase of the attack, a hacker can attempt toconnect to a mail server running on a well-known port number (e.g., mostSMTP mail servers run on port 25) A first entry can be stored in thedatabase (e.g., hash table) associated with this first phase of theattack. More particularly, a hash key derived from the source addressassociated with the potential hacker can be used to point to a record inthe hash table. At the time of the first attack, the record can bepopulated with a first entry indicating that a potential hacker from theidentified source address has contacted the mail server. During thesecond phase of the attack, a NIDS or a HIDS detects a exploitationattempt, e.g., a buffer overflow. The exploitation attempt is associatedwith a particular source, and accordingly, a check can be made in thehash table for a record associated with the source. More specifically,the source address is used to generate a key, which then is used to scanthe hash table for a matching entry. If matching record is located inthe database, then a second element can be added to the located recordto indicate that the source attempted a detected exploitation of thesystem. During the third phase of the attack, the mail server caninitiate a connection to the network, as the hacker controls the mailserver and successfully uses the mail server to send the hackerprotected information (e.g., a password file). If an attempt to gaincontrol of the mail server is detected, once again, the hash table canbe updated. More specifically, a key is derived from the address of thehacker that has been detected as attempting to take over the mailserver. The key is used to locate the appropriate record in the hashtable associated with the hacker. The third phase can result in thepopulation of a third element in the record associated with the hacker,indicative of the attempted take over of the mail server. At a time forevaluation, the sequence of attack events (port scan, exploitation, andmail server take over) can be recognized as a mail server attack and anappropriate response generated.

The invention can be implemented in digital electronic circuitry, or incomputer hardware, firmware, software, or in combinations of them. Theinvention can be implemented as a computer program product, i.e., acomputer program tangibly embodied in an information carrier, e.g., in amachine-readable storage device or in a propagated signal, for executionby, or to control the operation of, data processing apparatus, e.g., aprogrammable processor, a computer, or multiple computers. A computerprogram can be written in any form of programming language, includingcompiled or interpreted languages, and it can be deployed in any form,including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a communication network.

Method steps of the invention can be performed by one or moreprogrammable processors executing a computer program to performfunctions of the invention by operating on input data and generatingoutput. Method steps can also be performed by, and apparatus of theinvention can be implemented as, special purpose logic circuitry, e.g.,an FPGA (field programmable gate array) or an ASIC (application-specificintegrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for executing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto-optical disks, or optical disks. Information carrierssuitable for embodying computer program instructions and data includeall forms of non-volatile memory, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in special purposelogic circuitry.

The invention can be implemented in a computing system that includes aback-end component, e.g., as a data server, or that includes amiddleware component, e.g., an application server, or that includes afront-end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user can interact with animplementation of the invention, or any combination of such back-end,middleware, or front-end components. The components of the system can beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude a local area network (“LAN”) and a wide area network (“WAN”),e.g., the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

This invention has been described in terms of particular embodiments.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forinstance, the steps of the invention can be performed in a differentorder and still achieve desirable results. Instead of using hash tables,other equivalent data structures can be used. The hash tables can bestored using an SQL database. Accordingly, other embodiments are withinthe scope of the following claims.

1. A system comprising: a network device, that includes a processor and a memory, to: process, for detecting one or more attempted security breaches, each of a plurality of log records to generate a respective value corresponding to each of the plurality of log records, identify, based on the value corresponding to a log record of the plurality of log records, a first entry of a plurality of entries of a data structure, generate, based on one or more fields of the log record, a data value, associate the data value with a list of values associated with the first entry, when the data value does not match another value of the list of values, insert a tag into the first entry to form a modified entry after associating the data value with the list of values, analyze each of the plurality of entries of the data structure, identify, based on the tag of the first entry of the plurality of entries and the data value, the modified entry, perform, after identifying the modified entry, an evaluation of the data value associated with the modified entry to detect an attempted security breach, and modify, upon completion of the evaluation of the data value, the tag of the modified entry to cause the modified entry to no longer be identified as a modified entry.
 2. The system of claim 1, where, when modifying the tag, the network device is to: remove the tag from the modified entry.
 3. The system of claim 1, where the tag identifies the modified entry as having been modified during a particular period.
 4. The system of claim 3, where the particular period comprises a period defined by consecutive evaluations of the data structure.
 5. A method comprising: generating, by a network device and based on at least one field of a log record, a key; evaluating, by the network device, a data structure to identify an entry corresponding to the generated key; retrieving, by the network device, a data list associated with the identified entry; comparing, by the network device, the data list to a value, the value being generated using one or more fields of the log record; determining, by the network device, whether the data list includes a list entry that matches the value; inserting, by the network device and when the data list does not include the list entry that matches the value, the value into the data list; tagging, by the network device and when the data list does not include the list entry that matches the value, the identified entry in the data structure with a time stamp corresponding to the tagging; determining, by the network device and based on a tag associated with each entry of the data structure, whether each entry of the data structure is expired; deleting, by the network device, each expired entry of the data structure; evaluating, by the network device, each data list, associated with each unexpired entry of the data structure, to detect an attempted security breach; and generating, by the network device, a response to detecting the attempted security breach.
 6. The method of claim 5, where inserting the value comprises: inserting the tag into the identified entry in the data structure, the tag of the identified entry indicating that the data list, associated with the identified entry in the data structure, has been modified during a particular period, and where evaluating each data list associated with each unexpired entry comprises: determining whether each unexpired entry includes the tag; and evaluating each data list, associated with each unexpired entry of the data structure that includes the tag, to detect an attempted security breach.
 7. The method of claim 5, where inserting the value comprises: inserting a time stamp into the identified entry in the data structure, the time stamp being different than the tag associated with the identified entry.
 8. The method of claim 5, where evaluating each data list associated with each unexpired entry comprises: removing, upon evaluating the data list, the tag from the associated unexpired entry in the data structure.
 9. A method comprising: generating, by the network device and based on at least one field of a log record associated with a network event, a data value; identifying, by the network device and based on a particular value that is generated based on fields of the log record, a first entry in a data structure; comparing, by the network device, the generated data value to other data values, associated with the first entry in the data structure, to identify a matching data value corresponding to the generated data value; associating, by the network device and only when the generated data value does not match a data value in the other data values, the generated data value and a tag with the first entry in the data structure, the tag indicating that the first entry has been modified in the data structure; identifying, by the network device and based on the tag being associated with the first entry in the data structure, the first entry in the data structure as having been modified; evaluating, by the network device and based on identifying the first entry in the data structure as having been modified, the first entry in the data structure to detect an attempted security breach; and disassociating, by the network device and upon completion of the evaluating, the first entry, in the data structure, from the tag.
 10. The method of claim 9, where identifying the first entry comprises: determining, based on the tag, the first entry in the data structure as having been modified during a particular period.
 11. The method of claim 10, where the particular period comprises a period defined by consecutive evaluations of the data structure.
 12. The method of claim 9, where associating the generated data value and the tag comprises: inserting a time stamp into the generated data value, the time stamp being different than the tag.
 13. The method of claim 9, where the data structure comprises a plurality of entries including the first entry, and where identifying the first entry in the data structure as having been modified comprises: retrieving each of the plurality of entries; determining whether each of the plurality of entries is associated with a tag; evaluating, based on particular criteria, each of the plurality of entries determined to be associated with the tag to detect the attempted security breach; and disassociating, upon completion of evaluating each of the plurality of entries, the tag from each of the plurality of entries determined to be associated with the tag.
 14. The method of claim 9, where associating the tag with the first entry in the data structure comprises: inserting a tag into the first entry in the data structure.
 15. The method of claim 14, where disassociating the first entry in the data structure comprises: removing the tag from the first entry in the data structure.
 16. The method of claim 9, further comprising: receiving a plurality of individual log records, including the log record, upon each of the plurality of individual log records being generated; and processing each of the plurality of individual log records, upon being received, where processing the log record includes processing the log record to generate the data value.
 17. The method of claim 9, further comprising: receiving a record of logs, the record of logs identifying a plurality of individual log records including the log record; and retrieving, based on receiving the record of logs, the log record.
 18. A non-transitory computer-readable medium comprising: a plurality of instructions which, when executed by a device, cause the device to: process, for detecting one or more attempted security breaches, each of a plurality of log records to generate a respective value corresponding to each of the plurality of log records, identify, based on the value corresponding to a log record of the plurality of log records, a first entry of a plurality of entries of a data structure, generate, based on one or more fields of the log record, a data value, associate the data value with a list of values associated with the first entry, when the data value does not match another value of the list of values, insert a tag into the first entry to form a modified entry after associating the data value with the list of values, analyze each of the plurality of entries of the data structure; identify, based on the tag of the first entry, the modified entry; perform, after identifying the modified entry, an evaluation of the data value associated with the modified entry to detect an attempted security breach; and modify, upon completion of the evaluation of the data values, the tag of the modified entry to cause the modified entry to no longer be identified as a modified entry.
 19. The non-transitory computer-readable medium of claim 18, where one or more instructions, of the plurality of instructions, to modify the tag include: one or more instructions to remove the tag from the modified entry.
 20. The non-transitory computer-readable medium of claim 18, where the tag identifies the modified entry as having been modified during a particular period.
 21. The non-transitory computer-readable medium of claim 20, where the particular period comprises a period defined by consecutive evaluations of the data structure.
 22. The system of claim 1, where, when performing the evaluation of the data value associated with the modified entry to detect the attempted security breach, the network device is to: compare the data value to particular criteria; and detect the attempted security breach based on comparing the data value to the particular criteria.
 23. The system of claim 22, where the network device is further to: block, based on detecting the attempted security breach, packets from a source that is identified based on the log record.
 24. The non-transitory computer-readable medium of claim 18, where one or more instructions, of the plurality of instructions, to perform the evaluation of the data value associated with the modified entry to detect the attempted security breach, include: one or more instructions to identify, using the log record, a plurality of tests; and one or more instructions to perform the plurality of tests on the log record to detect the attempted security breach.
 25. The non-transitory computer-readable medium of claim 18, the plurality of instructions further comprising: one or more instructions to detect the attempted security breach based on the evaluation of the data value associated with the modified entry; and one or more instructions to block, based on detecting the attempted security breach, packets from a source that is identified based on the log record. 